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1. General Principles & Basic Science MCQs

Practice Set 256 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 5101

Topic: 1. General Principles & Basic Science

Which of the following zones of articular cartilage has the highest concentration of proteoglycans, the lowest concentration of water, and collagen fibrils oriented strictly perpendicular to the joint surface?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

Articular cartilage is divided into distinct zones. The deep (radial) zone contains the highest concentration of proteoglycans and the lowest concentration of water. The large-diameter collagen fibrils in this zone are oriented perpendicularly to the articular surface to provide maximal resistance to compressive forces.

Question 5102

Topic: Biology, Genetics & Bone Healing

In secondary fracture healing, the cartilaginous soft callus is eventually replaced by woven bone. Which of the following physiological processes predominantly facilitates this specific transformation?

. Intramembranous ossification
. Endochondral ossification
. Creeping substitution
. Appositional bone growth
. Chondrocyte transdifferentiation

Correct Answer & Explanation

. Endochondral ossification

Explanation

Secondary fracture healing occurs in stages: hematoma, soft callus (cartilage), hard callus (woven bone), and remodeling (lamellar bone). The transition from a cartilaginous soft callus to a woven bone hard callus occurs exclusively via endochondral ossification. Intramembranous ossification occurs directly subperiosteally without a cartilage intermediate.

Question 5103

Topic: Surgical Anatomy & Approaches

The anterior approach (Smith-Petersen) to the hip utilizes a true internervous plane. Which of the following best describes the specific internervous plane used in the superficial dissection of this surgical approach?

. Between the tensor fasciae latae (superior gluteal nerve) and the sartorius (femoral nerve)
. Between the gluteus medius (superior gluteal nerve) and the tensor fasciae latae (superior gluteal nerve)
. Between the rectus femoris (femoral nerve) and the vastus lateralis (femoral nerve)
. Between the adductor longus (obturator nerve) and the gracilis (obturator nerve)
. Between the gluteus maximus (inferior gluteal nerve) and the gluteus medius (superior gluteal nerve)

Correct Answer & Explanation

. Between the tensor fasciae latae (superior gluteal nerve) and the sartorius (femoral nerve)

Explanation

The superficial internervous plane of the anterior (Smith-Petersen) approach to the hip lies between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve). The deep plane is between the rectus femoris (femoral nerve) and the gluteus medius (superior gluteal nerve).

Question 5104

Topic: Infection, Pharmacology & VTE

A 45-year-old male is scheduled for open reduction and internal fixation of a closed tibial shaft fracture. He has a documented history of MRSA colonization and a severe anaphylactic allergy to penicillin (hives and shock). Which of the following is the most appropriate preoperative prophylactic antibiotic?

. Cefazolin
. Vancomycin
. Clindamycin
. Gentamicin
. Ceftriaxone

Correct Answer & Explanation

. Vancomycin

Explanation

For patients with a severe, IgE-mediated (anaphylactic) penicillin allergy, cephalosporins (like cefazolin and ceftriaxone) are generally avoided due to the small risk of cross-reactivity. Given the patient's documented history of MRSA colonization, Vancomycin is the definitive choice for preoperative prophylaxis to provide adequate coverage while avoiding an anaphylactic reaction.

Question 5105

Topic: Surgical Anatomy & Approaches
A 35-year-old male sustains an APC-III pelvic ring injury. During the ilioinguinal approach for anterior ring fixation, massive hemorrhage is encountered as the surgeon dissects near the superior pubic ramus. Which vascular anastomosis was most likely injured?
. External iliac artery and obturator vein
. External iliac vein and obturator artery
. Internal iliac artery and superior gluteal artery
. Inferior epigastric artery (or external iliac) and obturator artery
. External iliac artery and internal pudendal artery

Correct Answer & Explanation

. Inferior epigastric artery (or external iliac) and obturator artery

Explanation

The 'corona mortis' (crown of death) is a vascular anastomosis between the external iliac or inferior epigastric vessels and the obturator vessels. It is located over the superior pubic ramus, typically 4-9 cm from the pubic symphysis, and is at high risk of injury during the ilioinguinal approach or placement of superior pubic ramus screws, leading to massive hemorrhage.

Question 5106

Topic: 1. General Principles & Basic Science

Articular cartilage relies on a highly organized extracellular matrix for its biomechanical properties. Which zone of articular cartilage is characterized by the highest concentration of proteoglycans, the lowest concentration of water, and collagen fibers oriented perpendicular to the articular surface?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage has the highest proteoglycan content, the lowest water content, and thick type II collagen fibers arranged perpendicular to the joint surface. This structural arrangement is critical for resisting compressive forces.

Question 5107

Topic: Biology, Genetics & Bone Healing

A 28-year-old female presents with a lytic lesion in the distal femur. Biopsy confirms a Giant Cell Tumor (GCT) of bone. She is treated with Denosumab prior to planned surgical curettage to facilitate joint preservation. What is the precise mechanism of action of Denosumab?

. Monoclonal antibody that binds directly to RANK receptors on osteoclasts
. Monoclonal antibody that binds to RANKL, preventing it from activating RANK
. Tyrosine kinase inhibitor targeting VEGF
. Bisphosphonate analogue that induces osteoclast apoptosis
. Selective estrogen receptor modulator (SERM)

Correct Answer & Explanation

. Monoclonal antibody that binds to RANKL, preventing it from activating RANK

Explanation

Denosumab is a fully human monoclonal antibody that binds to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By binding to RANKL, it prevents RANKL from interacting with the RANK receptor on the surface of osteoclasts and their precursors, thereby inhibiting osteoclastogenesis and downregulating bone resorption. Giant cell tumors are rich in RANKL-expressing stromal cells.

Question 5108

Topic: 1. General Principles & Basic Science

A 45-year-old male sustains a posteromedial tibial plateau fracture. During a posteromedial surgical approach to the knee, the dissection plane is developed to access the fracture. Which two anatomical structures define the interval for this approach?

. Semitendinosus and Semimembranosus
. Medial head of the gastrocnemius and the pes anserinus (Semimembranosus)
. Popliteus and Soleus
. Sartorius and Gracilis
. Tibialis posterior and Flexor digitorum longus

Correct Answer & Explanation

. Medial head of the gastrocnemius and the pes anserinus (Semimembranosus)

Explanation

The posteromedial approach to the tibial plateau uses the internervous/intermuscular interval between the medial head of the gastrocnemius (retracted posteriorly/laterally) and the pes anserinus tendons, specifically the semimembranosus (retracted anteriorly/medially). This provides direct access to the posteromedial buttress of the tibia.

Question 5109

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a critical role in osteoinduction and are heavily utilized in spinal fusion. Recombinant human BMP-2 acts primarily through binding to cell surface receptors, initiating an intracellular signaling cascade. Which of the following molecules act as the primary intracellular signaling pathway for BMP-2?

. Wnt and beta-catenin
. JAK and STAT
. Smad 1, 5, and 8
. MAP kinase and ERK
. RANK and RANKL

Correct Answer & Explanation

. Smad 1, 5, and 8

Explanation

Bone morphogenetic proteins (BMPs) are members of the TGF-beta superfamily. They bind to serine/threonine kinase receptors on the cell surface, which then phosphorylate the receptor-regulated Smads (R-Smads), specifically Smad 1, 5, and 8. These complex with Smad 4 to enter the nucleus and regulate the transcription of osteogenic genes like Runx2.

Question 5110

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, what is the maximum strain tolerated by lamellar bone before failure?

. 2%
. 10%
. 30%
. 50%
. 100%

Correct Answer & Explanation

. 2%

Explanation

According to Perren's strain theory, different tissues tolerate different amounts of strain before tearing. Granulation tissue can tolerate up to 100% strain, fibrous tissue and cartilage tolerate around 10-15% strain, while lamellar bone is rigid and can only tolerate about 2% strain before failing.

Question 5111

Topic: Surgical Anatomy & Approaches
A 25-year-old male sustains an APC-III pelvic ring injury. During the surgical approach via the ilioinguinal approach, massive bleeding is encountered posterior to the superior pubic ramus. Which vascular structure is most likely injured?
. Internal pudendal artery
. Obturator artery
. Corona mortis
. Superior gluteal artery
. Inferior epigastric artery

Correct Answer & Explanation

. Corona mortis

Explanation

The corona mortis (crown of death) is a vascular anastomosis between the external iliac (or inferior epigastric) and obturator vessels. It is located posterior to the superior pubic ramus, roughly 4-6 cm from the symphysis pubis, and is at significant risk of iatrogenic injury during an ilioinguinal or modified Stoppa approach.

Question 5112

Topic: Infection, Pharmacology & VTE

Which of the following bacteria is most classically associated with the production of a dense glycocalyx (biofilm) that facilitates adhesion to orthopedic implants and resistance to antibiotics?

. Staphylococcus aureus
. Staphylococcus epidermidis
. Pseudomonas aeruginosa
. Streptococcus pyogenes
. Cutibacterium acnes

Correct Answer & Explanation

. Staphylococcus epidermidis

Explanation

Staphylococcus epidermidis (a coagulase-negative staphylococcus) is notorious for producing a thick exopolysaccharide layer known as a glycocalyx or biofilm. This slime layer allows it to adhere strongly to foreign bodies (such as arthroplasty components) and protects the bacteria from host immune responses and systemic antibiotics.

Question 5113

Topic: Surgical Anatomy & Approaches

During the classic volar Henry approach to the radius, the superficial surgical internervous plane lies between which two muscles?

. Flexor Carpi Radialis and Palmaris Longus
. Brachioradialis and Flexor Carpi Radialis
. Flexor Carpi Ulnaris and Flexor Digitorum Superficialis
. Extensor Carpi Radialis Brevis and Extensor Digitorum Communis
. Pronator Teres and Flexor Carpi Radialis

Correct Answer & Explanation

. Brachioradialis and Flexor Carpi Radialis

Explanation

The superficial internervous plane for the volar Henry approach is between the brachioradialis (innervated by the radial nerve) and the flexor carpi radialis (innervated by the median nerve).

Question 5114

Topic: Biomechanics & Biomaterials

Galvanic corrosion is most likely to occur in orthopedic surgery when which of the following combinations of metals are in direct physical contact within a conductive body fluid environment?

. Titanium alloy and commercially pure titanium
. Stainless steel and cobalt-chromium alloy
. Titanium alloy and cobalt-chromium alloy
. Stainless steel and titanium alloy
. Oxidized zirconium and cross-linked polyethylene

Correct Answer & Explanation

. Stainless steel and titanium alloy

Explanation

Galvanic corrosion occurs when two dissimilar metals with significantly different anodic indices are placed in contact within an electrolytic solution. The combination of stainless steel and titanium alloy leads to rapid galvanic corrosion of the stainless steel and should be avoided. Cobalt-chromium and titanium are closer on the galvanic series and are frequently used together safely.

Question 5115

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction during fracture healing and spinal fusion. Which of the following BMPs is also formally known as Osteogenic Protein-1 (OP-1)?

. BMP-2
. BMP-3
. BMP-4
. BMP-7
. BMP-9

Correct Answer & Explanation

. BMP-7

Explanation

BMP-7 is also known as Osteogenic Protein-1 (OP-1). It has been utilized commercially for nonunions and spinal fusions. BMP-2 is the active component in Infuse. BMP-3 actually has an inhibitory effect on bone formation.

Question 5116

Topic: Biomechanics & Biomaterials

Galvanic corrosion can occur in orthopaedic implants when two dissimilar metals are in contact within the body's electrolytic environment. If a stainless steel screw is used in a titanium alloy plate, which of the following accurately describes the electrochemical process that occurs?

. The titanium plate acts as the anode and undergoes accelerated corrosion.
. The stainless steel screw acts as the anode and undergoes accelerated corrosion.
. The titanium plate acts as the cathode and undergoes accelerated corrosion.
. The stainless steel screw acts as the cathode and is protected from corrosion.
. Both metals act as anodes and undergo equal rates of galvanic corrosion.

Correct Answer & Explanation

. The stainless steel screw acts as the anode and undergoes accelerated corrosion.

Explanation

In a galvanic couple, the less noble metal acts as the anode and corrodes, while the more noble metal acts as the cathode and is protected. Titanium is more noble (more cathodic) than stainless steel. Therefore, when they are mixed, the stainless steel screw acts as the anode and undergoes accelerated galvanic corrosion.

Question 5117

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with a lytic lesion in the distal femur extending to the subchondral bone. Biopsy confirms a Giant Cell Tumor (GCT) of bone. If medical therapy with Denosumab is initiated, what is the primary target and mechanism of action of this drug?

. It binds to RANKL on the neoplastic mononuclear stromal cells, preventing activation of RANK on osteoclast precursors.
. It binds directly to RANK on the multinucleated giant cells, inducing cellular apoptosis.
. It inhibits osteoprotegerin (OPG), thereby decreasing osteoclast differentiation.
. It stimulates osteoblast proliferation by binding directly to the Wnt signaling pathway.
. It directly inhibits matrix metalloproteinases secreted by the tumor cells.

Correct Answer & Explanation

. It binds to RANKL on the neoplastic mononuclear stromal cells, preventing activation of RANK on osteoclast precursors.

Explanation

In GCT of bone, the true neoplastic cells are the mononuclear spindle cells, which overexpress RANKL. This RANKL binds to RANK on normal macrophages, recruiting them and causing them to fuse into reactive multinucleated giant cells (osteoclast-like cells) that destroy bone. Denosumab is a monoclonal antibody that binds directly to RANKL on the neoplastic mononuclear cells, preventing it from activating RANK on the osteoclast precursors.

Question 5118

Topic: 1. General Principles & Basic Science

In the microscopic anatomy of articular cartilage, what is the primary structural and biomechanical function of the tidemark?

. It separates the superficial zone from the middle zone.
. It acts as a tethering zone between uncalcified cartilage and calcified cartilage.
. It represents the layer with the highest concentration of water and lowest proteoglycans.
. It serves as the primary barrier against the diffusion of synovial fluid into the superficial zone.
. It is the region where chondrocytes are metabolically most active for collagen type I synthesis.

Correct Answer & Explanation

. It acts as a tethering zone between uncalcified cartilage and calcified cartilage.

Explanation

The tidemark is a basophilic line visible on histology that delineates the boundary between the deep, uncalcified zone of articular cartilage and the calcified cartilage zone. Biomechanically, it serves as a critical mechanical tether that anchors the uncalcified cartilage to the underlying bone, resisting shear stress and preventing the propagation of microcracks.

Question 5119

Topic: Biomechanics & Biomaterials

In total hip arthroplasty (THA), the adoption of highly cross-linked polyethylene (HXLPE) has significantly reduced volumetric wear. What is the primary mechanical trade-off associated with increasing the radiation dose to maximize cross-linking during manufacturing?

. Increased oxidative degradation over time
. Decreased fatigue strength and fracture toughness
. Increased elastic modulus leading to stress shielding
. Decreased biocompatibility of the generated wear debris
. Increased risk of galvanic corrosion at the trunnion

Correct Answer & Explanation

. Decreased fatigue strength and fracture toughness

Explanation

Increasing the radiation dose during the manufacturing of HXLPE enhances cross-linking, which dramatically improves wear resistance. However, the primary mechanical consequence of this process is a notable decrease in the material's fatigue strength, tensile strength, and fracture toughness. This makes the polyethylene liner more susceptible to fracture, particularly if thin liners are used or if the component is malpositioned.

Question 5120

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs), particularly BMP-2 and BMP-7, play a pivotal role in osteoinduction during fracture healing. Which of the following intracellular signaling molecules are directly phosphorylated upon BMP binding to its cellular surface receptor?

. JAK/STAT
. Smad 1, 5, and 8
. beta-catenin
. c-Jun N-terminal kinase (JNK)
. Ras/MAPK

Correct Answer & Explanation

. Smad 1, 5, and 8

Explanation

BMPs exert their osteoinductive effects by binding to specific serine/threonine kinase receptors on the cell surface. This binding induces phosphorylation of intracellular receptor-regulated Smads (R-Smads), specifically Smad 1, 5, and 8. These phosphorylated Smads then complex with the common-mediator Smad 4 and translocate to the nucleus to upregulate transcription of osteogenic genes like Runx2.

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